Chemical vapor deposition methods are employed to form films of material on substrates such as wafers or other surfaces during the manufacture or processing of semiconductors. In chemical vapor deposition, a chemical vapor deposition precursor, also known as a chemical vapor deposition chemical compound, is decomposed thermally, chemically, photochemically or by plasma activation, to form a thin film having a desired composition. For instance, a vapor phase chemical vapor deposition precursor can be contacted with a substrate that is heated to a temperature higher than the decomposition temperature of the precursor, to form a metal or metal oxide film on the substrate. Preferably, chemical vapor deposition precursors are volatile, heat decomposable and capable of producing uniform films under chemical vapor deposition conditions.
The semiconductor industry is currently considering the use of thin films of various metals for a variety of applications. Many organometallic complexes have been evaluated as potential precursors for the formation of these thin films. A need exists in the industry for developing new compounds and for exploring their potential as chemical vapor deposition precursors for film depositions.
Molybdenum materials are being considered for a number of applications in the electronics industry for next generation devices, including electrode, barrier, and lithography. Similar to the interest in tuning a material by creating an alloy of a n-type and p-type metal in different ratios (as exemplified by the work by Misra V. et al. at North Carolina State (IEDM 2001 20.5.1)), molybdenum can be tuned with nitrogen incorporation and/or deposition orientation to generate a similar effect (with the advantage of a single, less expensive source). The work function of molybdenum can thus be adjusted significantly (Fonseca, L. R. C., Fall MRS E4.3, 2003 and Mrovek, M., Fall MRS E4.2, 2003).
Another interest in molybdenum materials is for barrier applications (e.g., Cu). Molybdenum nitrides are candidates for this application (Gordon R. et al., Thin Solid Films 1996 288 116). Molybdenum films also have applications in the area of lithography, with potential utility for the engineering of projection lens systems for photolytical patterning of substrates for extreme ultra-violet lithography (EUVL) at the 45 nm technology node (Van den hove, L. IEEE 2002).
The industry movement from physical vapor deposition to chemical vapor deposition and atomic layer deposition processes due to the increased demand for higher uniformity and conformality in thin films has lead to a demand for suitable precursors for future semiconductor materials. For molybdenum, the traditional chemical vapor deposition precursors have been Mo(CO)6 and (EtxC6H6−x)2Mo (a mixture of bis(ethylbenzene)molybdenum species). The former suffers from being a solid up to its decomposition point of 150° C., and the latter, although a liquid, does not have a high vapor pressure (˜0.1 torr at 160° C.) and may deliver inconsistently due to the various species present.
(C7H8)Mo(CO)3 is also available, but is a solid (mp=100° C.), and lacks sufficient thermal stability to be a highly desirable candidate.
Building from Mo(CO)6, replacing three CO's with a cyclopentadienyl (Cp) group seems logical since many Cp systems are known chemical vapor deposition precursors and Cp allows excellent tunability for achieving liquid systems. However, [CpMo(CO)3]− exists as an anion, and therefore is not sufficiently volatile (note, the dimer of this system is neutral, but has little volatility due to the increased molecular weight). Changing Cp to a similar neutral six electron donor would seem a logical progression, thus yielding the aforementioned (C7H8)Mo(CO)3. Although this compound is neutral with perhaps adequate volatility, the other issue with these tricarbonyl systems is their instability. The lack of enough strong π-acids, like CO, render the material very electron rich, and make the complex susceptible to premature decomposition. Two potential pathways are a ‘ring-slip’ for the cycloheptatriene ligand from an η6 six electron donor to an η4 four electron donor (alleviating the electron density on molybdenum) or loss of a hydride from the cycloheptatriene ligand creating an aromatic system and creating a less donating environment and a molybdenum cation. Another known molecule, (C6H6)Mo(CO)3, suffers from similar instability issues.
While the unsubstituted cyclopentadienyl compound, i.e., CpMo(CO)2(NO), and the methyl substituted cyclopentadienyl compound, i.e., (MeCp)Mo(CO)2(NO), are known materials (Legzdins, P. et al. Inorg. Synth. 1990, 28, 196 and references therein and Rausch, M. D. et al. Organometallics 1983, 2, 1523 and references therein), there appear to be no prior teachings or work relating to the use of these compounds as precursors for chemical vapor deposition or atomic layer deposition.
In developing methods for forming thin films by chemical vapor deposition methods, a need continues to exist for chemical vapor deposition precursors that preferably exhibit dual metal gate applications, are liquid at room temperature, have relatively high vapor pressure and can form uniform films. Therefore, a need continues to exist for developing new compounds and for exploring their potential as chemical vapor deposition precursors for film depositions. It would therefore be desirable in the art to provide a chemical vapor deposition precursor having dual metal gate applications, a high vapor pressure and that can form uniform films.